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Panther Series - CGS735 Synthacon Filter 




The Panther CGS7xx Series are authorised re-releases of the popular 
Cat Girl Synth Series of modules from Ken Stone. Each module is 
revisited to determine if any improvements can be added to the original 
design which has also been adjusted, where applicable, to fit the 
smaller profile of the EuroRack module size. 



The CGS735 Synthacon Filter 

This module is a "tribute" module, based on the awesome Steiner-Parker Synthacon VCF. 
How to use this module 



© 


CGS735 


© 




Synthacon Filter 


# 


# 


4 J 6 


ALL IN 


CVIN 


CV LEVEL 


# 


4 5 6 


4 J 6 

o 


HIGHPASS 


HP LEVEL 


RESONANCE 





Connect the CV input to a voltage source such as a keyboard, 
envelope generator or sequencer. Connect the output to a VCA 
or amplifier. Feed the signal to be filtered into the high-pass, 
band-pass or low-pass input. If the same signal is used in all 
inputs, the result is reminiscent of a phaser. The real fun starts 
when you feed different signals into each input, then you get a 
frequency based "interpolating scanner", where panning between 
different sound sources is possible, though also subject to the 
frequency at which they are running. 

Each of the filter type inputs has its own level control. The ALL 
input is also affected by these level pots as it is mixed with the 
individual inputs prior to the level controls. If using only a single 
input, it may be better to feed the signal into the ALL input, and 
adjust the level pots to select LP, BP or HP, rather than changing 
the patch cord between the specific input jacks. 

A little on how it works 

The circuit uses a standard, non-inverting amplifier configuration. 
The three modes (HP=High-Pass, BP=Band-Pass, LP=Low- 
Pass) are obtained by injecting the signal into three different 
points of the circuit. An increase in the gain of the amplifier 
increases the filter's Q. The Q remains almost constant as the 
filter is swept across the audio spectrum. In the circuit, diode 
strings are used as voltage controlled resistors. 

The differential-amplifier transistors apply the bias voltage to the parallel diode string RC networks in 
opposing phase. The opposing phases cancel the control voltage so that none appears at the output. The 
final pair of transistors form a non-inverting amplifier. The RESONANCE pot adjusts the gain of this amplifier, 
and thus its Q. 

The final stage is a simple gain stage. 



BANDPASS 



2 \ J!* H \^ ; s 

BP LEVEL FREQUENCY 




LOWPASS 





OUT 



© ELBY DESIGNS -KEN STONE © 



Power Requirements 


+12V @15mA, -12V @ 13ma 


Module Width 


14HP 



Elby Designs - Laurie Biddulph 

9 Follan Close, Kariong, NSW 2250, Australia 
elby designs@ozemail.com.au http://www.elby-designs.com 

lof 2 






Designs 



Panther Series - CGS735 Synthacon Filter 



Inside the CGS735 




Rear view showing the Panther Support boards 




The main board in the CGS735 



9 CGS735 

Synthacon Filter 



ALL IN WIN 



h 

■9 



CV LEVEL 



HIGHPASS 



BANDPASS 



r s2 \ > 

*9 1'-J^^P"9 
HP LEVEL RESONANCE 

4 ? 6 

BP LEVEL FREQUENCY 

4 ; 6 

• o 

LOWPASS OUT 

LP LEVEL 



ffi ELBYDESIGNS -KEN STONE © 



4mm Banana Socket version 



Elby Designs - Laurie Biddulph 

9 Follan Close, Kariong, NSW 2250, Australia 
elby designs@ozemail.com.au http://www.elby-designs.com 

2 of 2 



Designs